1. Field of the Invention
The present disclosure relates to a zoom lens and an image pickup apparatus, such as a video camera, a monitoring camera, a digital still camera, or a broadcasting camera, quipped with the zoom lens.
2. Description of the Related Art
A zoom lens used in an image pickup apparatus, such as a video camera or a monitoring camera, is required to have a large aperture, to be able to easily perform image shake correction, and to contribute to miniaturization of a lens barrel structure.
Japanese Patent Application Laid-Open No. 2007-052374 discusses a zoom lens including, in order from an object side to an image side, a first lens unit having positive refractive power, a second lens unit having negative refractive power, a third lens unit having positive refractive power, and a fourth lens unit having positive refractive power, in which the third lens unit is divided into a first lens sub-unit having positive refractive power and a second lens sub-unit having negative refractive power, and image shake correction is performed by the first lens sub-unit, which is composed of a single positive lens. Such a four-unit zoom lens discussed in Japanese Patent Application Laid-Open No. 2007-052374 performs image shake correction by using one lens element, thus achieving miniaturization of the entire image pickup apparatus. However, since an axial light flux is made into a diverged light flux by the second lens unit having negative refractive power to be incident on the third lens unit, an effective aperture of the single lens that performs image shake correction cannot be sufficiently reduced in diameter.
Japanese Patent Application Laid-Open No. 2005-148437 discusses a zoom lens including, in order from an object side to an image side, a first lens unit having positive refractive power, a second lens unit having negative refractive power, a third lens unit having positive refractive power, and a fourth lens unit having positive refractive power, in which the third lens unit is divided into a first lens sub-unit having positive refractive power, a second lens sub-unit having negative refractive power, and a third lens sub-unit, and image shake correction is performed by the second lens sub-unit, which is a single lens having negative refractive power. in such a four-unit zoom lens discussed in Japanese Patent Application Laid-Open No. 2005-148437, since image shake correction is performed moving only the second lens sub-unit while fixing the first lens sub-unit and the third lens sub-unit, a lens barrel structure is complicated, and as a result, miniaturization cannot be significantly achieved.